Two-component in-situ curing wear-resistant coating process for polycarbonate transparent plate

Abstract

The invention provides a double-component in-situ curing wear-resistant coating process of a polycarbonate transparent plate, and relates to the technical field of polycarbonate plates. The preparation process of the double-component in-situ curing wear-resistant coating for the polycarbonate transparent plate comprises the processes of double-component coating preparation, vacuum-assisted in-situ injection and gradient heating segmented curing. According to the invention, the hardness, adhesive force and optical transparency of the coating are comprehensively improved by adopting the two-component acrylic polyurethane system and the thermal latent catalyst and cooperating with the vacuum-assisted in-situ forming and gradient heating segmented curing process, and the coating has a good application prospect.

Description

Technical Field

[0001] This invention relates to the field of polycarbonate sheet technology, and more particularly to a two-component in-situ curing wear-resistant coating process for transparent polycarbonate sheets. Background Technology

[0002] Polycarbonate (PC) is widely used in aerospace, automotive, and electronic communications fields due to its excellent light transmittance, impact resistance, and processing properties. However, PC has low surface hardness, making it highly susceptible to physical wear and scratches, which reduces its lifespan and optical performance. Current wear-resistant coating processes mostly employ spraying, curtain coating, or traditional injection compression molding. These processes often suffer from poor coating thickness uniformity, significant environmental pollution, easy generation of surface defects (such as pinholes and shrinkage cavities), and insufficient adhesion between the coating and the substrate due to excessive internal stress, severely limiting the application of PC sheets in high-precision optics.

[0003] Therefore, it is necessary to provide a process for preparing wear-resistant coatings for PC transparent sheets that can achieve a balance between high hardness, high adhesion and high optical performance. Summary of the Invention

[0004] In view of this, the present invention provides a two-component in-situ curing wear-resistant coating process for transparent polycarbonate sheets. By employing a two-component acrylic polyurethane system with a thermally latent catalyst, and combining it with vacuum-assisted in-situ molding and gradient temperature staged curing processes, the present invention achieves a comprehensive improvement in coating hardness, adhesion, and optical transparency, demonstrating promising application prospects.

[0005] A process for preparing a two-component in-situ cured wear-resistant coating for transparent polycarbonate sheets includes the following steps: S1. Two-component coating preparation: Mix component A and component B to obtain a two-component reactive coating; Component A is a mixture of acrylic polyol resin and leveling agent; Component B is a mixture of isocyanate curing agent and heat-latent catalyst; S2, Vacuum-assisted in-situ injection: A cavity is constructed between the PC substrate and the mold panel. Before the coating is injected, the sealed cavity is vacuumed so that the coating is filled by vacuum in the gap and self-levels to form a coating. The two-component coating is injected into the cavity through a multi-point distributed feed port. Vacuum-assisted in-situ injection drives filling through pressure difference, avoiding high-pressure injection shear stress and promoting the escape of microbubbles in the coating before curing; S3. Gradient temperature segmented curing: The coating formed in step S2 is pre-cured and fully cured sequentially. Preferably, in step S1, the hydroxyl value of the acrylic polyol resin is 30-120 mg KOH / g, more preferably 50-90 mg KOH / g; the leveling agent is at least one of silicone-modified polyether leveling agent, acrylic leveling dispersant leveling agent, and fluorocarbon surfactant leveling agent; the leveling agent accounts for 0.05%-1.0% of the mass of component A; the NCO content of the isocyanate curing agent is 10%-25%; the thermally latent catalyst is a thermally latent tertiary amine catalyst, used to reduce the reaction rate in the pre-curing stage at 60-80℃ and promote the crosslinking reaction in the complete curing stage at 120-140℃; the thermally latent catalyst accounts for 0.01%-0.5% of the mass of component B. More preferably, the thermally latent catalyst is DBU-1-naphthoate.

[0006] Preferably, the preparation method of the DBU-1-naphthoate thermally latent catalyst is as follows: 1-Naphthoic acid was placed in a vacuum drying oven and dried at 60℃ and -0.09 MPa for 2 h to remove the adsorbed moisture from the raw material. Strict control of moisture is a key prerequisite for avoiding side reactions with the isocyanate system and ensuring the potential of the catalyst. The raw materials are accurately weighed according to the ratio of organic acid to DBU of 1.0:(0.9-1.1). The pretreated 1-naphthoic acid is added to a dry reaction vessel, and the metered anhydrous solvent is added. The mixture is stirred at room temperature (25°C) or 40°C in a water bath until completely dissolved to form a clear and transparent organic acid solution. More preferably, the molar ratio of organic acid to DBU is 1:1. Under constant temperature and stirring conditions of 25-40℃, DBU was slowly added dropwise to the organic acid solution at a rate of 1-2 mL / min, while maintaining a stirring rate of ≥300 rpm during the addition. After the addition was completed, the mixture was stirred at a constant temperature for 30-60 min to ensure that the acid and base fully underwent the protonation and salt formation reaction. Cool the reaction system to 0-10℃ and let it stand for 30 min to promote the crystallization of tertiary amine organic acid salts from the solvent; if no obvious crystallization occurs, the system can be concentrated by vacuum distillation until turbidity appears, and then cooled and allowed to stand to complete the crystallization. Collect the crystalline solid by vacuum filtration, and wash the solid twice with anhydrous solvent at 0-5℃, with the amount of solvent used each time being 30%-50% of the solid mass, in order to remove free organic acids and tertiary amines adsorbed on the solid surface.

[0007] The washed solid was placed in a vacuum drying oven and dried at 40-60℃ and -0.09 MPa for 4-8 h to obtain the DBU-1-naphthoate thermal latent catalyst.

[0008] Preferably, in step S1, the two-component reactive coating has a viscosity of 500-1000 mPa·s at 25°C, more preferably 600-900 mPa·s, and an NCO / OH equivalent ratio of 0.95-1.10, more preferably 1.00-1.05; before mixing component A and component B, they are respectively allowed to stand at 25°C for degassing for ≥10 min, and the mixing is carried out by low-shear stirring at a speed of 300-800 rpm for 3-8 min; after mixing, vacuum degassing can be performed at -0.06~-0.09 MPa for 1-5 min to prevent residual bubbles in the subsequent mold cavity.

[0009] Preferably, in step S2, the cavity gap is 0.3-0.8 mm, and the thickness deviation is ±0.05 mm; the vacuum degree of the sealed cavity is -0.08 MPa to -0.1 MPa. Preferably, in step S3, the pre-curing temperature is 60-80℃, held for 10-15 minutes, for leveling and stress release; the complete curing temperature is 120-140℃, held for 30-45 minutes, for deep cross-linking and hardening. The complete curing temperature and holding time can be adjusted within a range according to the PC thickness and mold thermal conductivity to avoid warping / yellowing. This invention does not limit the heating rate; conventional temperature control methods in the art can be used to achieve the two-stage processing temperature.

[0010] Compared with the prior art, the beneficial technical effects of the present invention are as follows: This invention employs a vacuum-assisted in-situ injection method, utilizing pressure difference to drive the coating material to fill a precision cavity. This effectively avoids the shear stress and stress concentration problems caused by traditional high-pressure injection, ensuring extremely high tolerance accuracy of the coating thickness.

[0011] This invention achieves precise control of the polymerization reaction rate by introducing a thermally latent tertiary amine catalyst: during the room temperature and pre-curing stages, the system maintains low activity, providing a sufficient time window for the coating to fully level and for microbubbles to escape completely; during the fully cured stage, it rapidly releases activity to promote deep cross-linking, ensuring that the coating obtains excellent surface hardness and wear resistance.

[0012] The gradient temperature curing process of this invention can effectively release the interfacial stress between the coating and the substrate during the pre-curing stage, greatly enhancing the adhesion between the coating and the PC substrate and solving the process problem of easy peeling of high-hardness coatings.

[0013] The fully enclosed processing environment of this invention not only improves the environmental friendliness of the production process, but also significantly reduces the impact of environmental dust on optical quality. Attached Figure Description

[0014] The present invention will be further described below with reference to the accompanying drawings.

[0015] Figure 1 This is a flow chart illustrating the preparation process of the two-component in-situ cured wear-resistant coating for polycarbonate transparent sheets according to the present invention. Detailed Implementation

[0016] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0017] Unless otherwise stated, all raw materials used in the examples are commercially available industrial products; all viscosities were measured using a rotational viscometer at 25°C (Brookfield method); and the "vacuum degree" is a negative pressure value relative to atmospheric pressure.

[0018] In the following embodiments and comparative examples of the present invention, the DBU-1-naphthoate thermally latent catalyst (hereinafter referred to as "latent catalyst") was prepared by the following method: 1-Naphthoic acid was dried at 60℃ and -0.09 MPa for 2 h. The dried 1-naphthoic acid was dissolved in anhydrous ethanol and DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) was slowly added dropwise at an acid-base molar ratio of 1:1 under stirring at 25℃. The addition was accelerated at a rate of 1.5 mL / min. After the addition was completed, the mixture was stirred at a constant temperature for 45 min. The mixture was then cooled to 5℃ and allowed to stand to crystallize. The crystals were filtered under reduced pressure and washed twice with cold anhydrous ethanol. Finally, the mixture was dried under vacuum at 50℃ for 6 h to obtain a white crystalline solid.

[0019] Unless otherwise specified, all experiments were repeated three times. Results are expressed as mean ± standard deviation, and P < 0.05 indicates a significant difference.

[0020] Example 1: A preparation process for a two-component in-situ cured wear-resistant coating on a transparent polycarbonate sheet, comprising the following steps: S1. Two-component coating formulation: Component A: Select 100 g of acrylic polyol resin with a hydroxyl value of 70 mg KOH / g, and add 0.5 g of organosilicon modified polyether leveling agent (BYK-333) (accounting for 0.5% of the mass of component A). Component B: Select HDI trimer isocyanate curing agent with NCO content of 18%, and add 0.05 g of the above-prepared latent catalyst (accounting for 0.1% of the mass of component B). Components A and B were weighed according to an NCO / OH equivalent ratio of 1.02. Before mixing, they were allowed to stand at 25°C for 15 min to degas. Component B was added to component A and stirred at 500 rpm under low shear for 5 min, followed by vacuum degassing at -0.08 MPa for 3 min. The initial viscosity of the mixed coating at 25°C was measured to be 750 mPa·s. S2. Vacuum-assisted in-situ injection: Construct a sealed cavity consisting of a PC substrate and a high-gloss glass mold panel. Set the cavity gap to 0.5 mm. Start the vacuum pump to evacuate the cavity, so that the vacuum degree inside the cavity reaches -0.09 MPa. Utilize the pressure difference to draw the above-mentioned two-component coating into the cavity through a multi-point distributed feed port. Rely on vacuum drive and gravity assistance to achieve rapid filling and self-leveling. S3, Gradient temperature rise and segmented curing: Pre-curing: Place the mold assembly filled with paint in an oven, heat it to 70°C and keep it at that temperature for 12 minutes; Complete curing: Then heat to 130°C and hold for 40 minutes; After natural cooling, the material is demolded to obtain a transparent polycarbonate sheet with a wear-resistant coating.

[0021] Example 2 The difference from Example 1 is that in step S1, the amount of thermally latent catalyst added is adjusted to 0.02% of the mass of component B.

[0022] Example 3 The difference from Example 1 is that in step S1, an acrylic polyol resin with a hydroxyl value of 110 mg KOH / g is selected; the amount of isocyanate curing agent is adjusted accordingly to maintain the NCO / OH equivalent ratio of 1.05.

[0023] Example 4 The difference from Example 1 is that in step S3, the pre-curing temperature is set to 60°C and held for 15 minutes; the complete curing temperature is set to 120°C and held for 45 minutes.

[0024] Comparative Example 1 The difference from Example 1 is that the latent catalyst in step S1 is replaced with an equimolar amount of ordinary DBU (liquid, unsealed).

[0025] Comparative Example 2 The difference from Example 1 is that the pre-curing stage in step S3 is omitted, and the temperature is directly raised to 130°C and held for 50 minutes after injection molding.

[0026] Comparative Example 3 The difference from Example 1 is that: in step S2, the cavity is not vacuumed, and the coating is injected into the cavity using a traditional high-pressure injection machine with an injection pressure of 5 MPa.

[0027] Comparative Example 4 The difference from Example 1 is that in step S1, the NCO / OH equivalent ratio is adjusted to 0.80.

[0028] Comparative Example 5 The difference from Example 1 is that in step S3, the pre-curing conditions are adjusted to: temperature 100℃, held for 15 minutes.

[0029] Comparative Example 6 The difference from Example 1 is that in step S3, the conditions for complete curing are adjusted to: temperature 100°C, held for 45 minutes.

[0030] All embodiments and comparative examples were tested uniformly, and the results are shown in Table 1.

[0031] Table 1 Performance test results of each embodiment and comparative example

[0032] Note: Different superscript letters in the same column indicate significant differences (P<0.05).

[0033] Comparing the data in Table 1, it can be seen that the coating prepared by the process of this invention has excellent mechanical and optical properties, and the overall quality meets the standard requirements. Comparative Example 1, due to the replacement of the catalyst with an active catalyst, experienced an excessively rapid reaction, leading to leveling failure, a drop in transmittance to 88.5%, and the appearance of flow marks. Comparative Example 2 lacked a pre-curing step, resulting in the inability to release internal stress, causing the adhesion to drop to level 3 and warping to occur. Comparative Example 3 used high-pressure injection, which could not effectively eliminate microbubbles, leading to a thickness deviation of ±0.12 mm, severely affecting optical quality and dimensional accuracy. This demonstrates that only through the synergistic effect of these three factors can the leveling, stress, and bubble problems be solved simultaneously.

[0034] When the NCO / OH equivalent ratio is as low as 0.8 (Comparative Example 4), the cross-linking network cannot be effectively established, resulting in a sharp drop in hardness to H and almost no abrasion resistance. If the pre-curing temperature is too high, reaching 100℃ (Comparative Example 5), premature reaction will lock in air bubbles, reducing light transmittance and damaging adhesion. If the complete curing temperature is insufficient (Comparative Example 6), the catalyst cannot be desealed, the coating is not completely dry, the hardness is only HB, and the abrasion resistance test fails.

[0035] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A preparation process for a two-component in-situ cured wear-resistant coating on a transparent polycarbonate sheet, characterized in that, Includes the following steps: S1. Formulation of two-component coating: Mix component A and component B to obtain a two-component reactive coating. The two-component reactive coating has a viscosity of 500-1000 mPa·s at 25°C and an NCO / OH equivalent ratio of 0.95-1.

10. Component A is a mixture of acrylic polyol resin and leveling agent; Component B is a mixture of isocyanate curing agent and heat-latent catalyst; S2, Vacuum-assisted in-situ injection: A cavity is constructed between the PC substrate and the mold panel. Before the coating is injected, the sealed cavity is vacuumed and the two-component coating is injected into the cavity through a multi-point distributed feed port. S3. Gradient temperature segmented curing: The coating formed in step S2 is pre-cured and fully cured sequentially. The pre-curing temperature is 60-80℃, held for 10-15 minutes, for leveling and stress release; the complete curing temperature is 120-140℃, held for 30-45 minutes.

2. The preparation process according to claim 1, characterized in that, In step S1, the hydroxyl value of the acrylic polyol resin is 30-120 mg KOH / g.

3. The preparation process according to claim 1, characterized in that, In step S1, the hydroxyl value of the acrylic polyol resin is 50-90 mg KOH / g.

4. The preparation process according to claim 1, characterized in that, In step S1, the leveling agent is at least one of silicone-modified polyether leveling agent, acrylic leveling dispersion leveling agent, and fluorocarbon surfactant leveling agent, and the leveling agent accounts for 0.05%-1.0% of the mass of component A.

5. The preparation process according to claim 1, characterized in that, In step S1, the leveling agent accounts for 0.05%-1.0% of the mass of component A.

6. The preparation process according to claim 1, characterized in that, In step S1, the NCO content of the isocyanate curing agent is 10%-25%; the thermally latent catalyst is a thermally latent tertiary amine catalyst.

7. The preparation process according to claim 6, characterized in that, The thermally latent tertiary amine catalyst is DBU-1-naphthocarbamate.

8. The preparation process according to claim 1, characterized in that, In step S1, the thermally latent catalyst accounts for 0.01%-0.5% of the mass of component B.

9. The preparation process according to claim 1, characterized in that, In step S1, the two-component reactive coating has a viscosity of 600-900 mPa·s at 25°C and an NCO / OH equivalent ratio of 1.00-1.

05.

10. The preparation process according to claim 1, characterized in that, In step S2, the cavity gap is 0.3-0.8 mm, the thickness deviation is ±0.05 mm, and the vacuum degree of the sealed cavity is -0.08 MPa to -0.1 MPa.

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